Getting really bad accuracy from CLLocationManager - ios

Question

I'm using CLLocationManager to get users location.
I want to get a single location update.
My problem is that I'm getting really bad horizontalAccuracy
location is %# <+xx.xxxxxx,+yy.yyyyyyy> +/- 3881.91m
verticalAccuracy: 65.4401861912846, horizontalAccuracy: 3881.90892434957
Code:
fileprivate lazy var locationManager: CLLocationManager = {
let manager = CLLocationManager()
manager.desiredAccuracy = kCLLocationAccuracyBest
manager.delegate = self
manager.requestAlwaysAuthorization()
manager.pausesLocationUpdatesAutomatically = false
manager.desiredAccuracy = kCLLocationAccuracyBest
manager.distanceFilter = kCLDistanceFilterNone
return manager
}()
override init() {
super.init()
locationManager.startUpdatingLocation()
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
guard let mostRecentLocation = locations.last else {
return
}
let verticalAccuracy = mostRecentLocation.verticalAccuracy
let horizontalAccuracy = mostRecentLocation.horizontalAccuracy
print("location is %#", mostRecentLocation)
print("verticalAccuracy: \(verticalAccuracy), horizontalAccuracy:\(horizontalAccuracy)")
}
Any suggestions why is this happening?
I'm in a room next to a window so i except to get bad accuracy but not that bad.
Thanks
I'm getting ridiculous results.
I got horizontalAccuracy of 15,000 m.
When i go out doors it works great but in doors should not be as bad as this.
Using Cellular triangulation and wifi should give a lot better results.
after 20 minutes i started to get good results of +- 50 m accuracy in doors.

Answer 1

I suggest you add a condition to make sure that you will just be using a location that have a better accuracy. On my case I use 20 as the desired horizontal accuracy on below example.
Example:
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
locationManager.stopUpdatingLocation()
if locations.last!.horizontalAccuracy < 20 {
//Only use location that enters here
}
else {
//If the accuracy is not met then start updating location again and if possible increase more the accuracy (use kCLLocationAccuracyBestForNavigation if you really need it). Make sure that you use the desired accuracy and filter properly to avoid draining battery.
locationManager.startUpdatingLocation()
}
}

Answer 2

I always have found that when you first start location updates, the first few readings are quite poor, and then the accuracy improves as the GPS settles down.
What I do is to first check if the timestamp on the location is more than a few seconds old. If it is, I discard it. (Not sure if recent OS versions still send "stale" GPS readings, but the system used to give you a location from the last time the GPS was powered up, sometimes several hours old.)
Once I get current locations, I check the accuracy, and discard any location updates who's accuracy reading is too poor. Only when I get a reading that's good enough do I use it (and stop location updates in your case, since you only want 1 update.)
Bear in mind that it can take 30 seconds (or more) for the GPS to settle down, and in an area with poor GPS signal, you may never get a good enough reading.